Should journalists honour their word to a mass murderer?

I have just set my City University students their winter assignments and one of the questions concerns the ethical dilemma faced by a journalist who had to decide whether to breach the confidentiality of a source who had confessed to a murder.

I say the same, but Nuon Chea – as second-in-command to the Cambodian despot Pol Pot – was responsible for the killing of many hundreds of thousands of people.

And he confessed his part in mass murder to the Cambodian journalist, Thet Sambath, on the condition that it could only be used as a historical record. It must not be used against him.

Sambath agreed, and went on to interview Chea in such detail that he recorded some 160 hours of filmed footage.

Then, together with an English-based film producer, Rob Lemkin, he made a film Enemies of the People, described as "one man's journey into the heart of the killing fields."

The film, which has won seven festival awards, is due to be shown in British cinemas from 10 December.

Now the United Nations has requested that Sambath and Lemkin hand over all their original footage to be used as evidence in next year's trial of 84-year-old Chea for genocide. They have refused, explaining that they are honouring their promise to Chea.

But is it right to honour a promise to a man who has admitted such heinous crimes?

Lemkin says: "It's essential as a journalist or filmmaker, that if you give an assurance, you don't change the goal posts after you've made the film."

And Sambath says: "I don't think revenge is good for anyone. My work was focused on gaining as complete an account of the Killing Fields as I could. Revenge has no part in that.

"I think the court is focused on justice, which is okay. But I think reconciliation would be a better end result. For reconciliation to take place we need first the truth."

It is thought that Pol Pot's Khmer Rouge murdered 2m people between 1975 and 1979. Among them were Sambath's own family.